def quickSort(li,start,end):
    if start >= end:
        return
    mid = li[start]
    low = start
    high = end
    while low < high :
        while low < high and li[high] >= mid:
            high -= 1
        li[low] = li[high]
        while low < high and li[low] < mid:
            low += 1
        li[high] = li[low]
    li[low] = mid
    quickSort(li,start,low -1)
    quickSort(li,low+1,end)

alist = [54,26,93,17,77,31,44,55,20]
# alist = [17,26,20]

quickSort(alist,0,len(alist)-1)
print(alist)